The present invention relates to a screw-type pumping unit for treatment of fluids in several phases.
In particular, in this case, reference is made to a screw-type pumping unit which can be used in the exploitation of oil fields, and which must therefore be able to treat simultaneously multi-phase mixtures consisting in particular of crude oil in the liquid phase, and its accompanying gases.
A problem which is applicable in particular consists of the fact that the oil fields which are known at present are not all exploited. In fact, only the fields which are economically viable and have a certain size, combined with quality products, are actually exploited, and the other fields which are not economically viable are considered as xe2x80x9cmarginal fieldsxe2x80x9d.
The marginal fields are usually located in inconvenient areas on land, or, increasingly frequently, they are in undersea areas, in waters of medium depths.
The development of the marginal fields is considered to be one of the determining factors in the international oil industry in the near future. This aspect is applicable in particular in the case of undersea fields, since at present, oil research is being carried out specifically in this respect.
On this understanding, particular reference will be made hereinafter to a pumping unit which can be used for extraction of crude oil from underground fields.
However, it should be understood that the present invention can be used in other, different applications, such as also in an oil field on land, in a particularly inconvenient environment.
In order to assist understanding of the present invention, it should be noted that the conventional techniques of extraction of crude oil from an oil field require that the fluid extracted from the wells is firstly separated in the vicinity of the head of the wells, into its liquid and gaseous components, which are subsequently conveyed by means of pipes or tankers to an oil processing centre. The oil processing centre is usually located on land or on a production rig, and therefore at a distance from the well which can actually be considerable.
It will be appreciated that this makes the process of extraction and subsequent treatment of the crude oil extremely costly, and means that, as already stated, many fields are considered as marginal fields, and are therefore not exploited owing to the high costs which this would involve.
However, in recent years, a new production technique has been developed, consisting of extraction and conveyance of the multi-phase mixture, as extracted from the wells, to the processing centres, where it is treated. This therefore provides a substantial decrease in costs, which makes many fields which were previously considered marginal economically viable.
In order to implement the production technique described, pumping units have been developed which can carry out simultaneously both the service of thrusting the liquids, and compressing the gases.
In order to make apparent the technical problems which are inherent in simultaneous pumping and compression of a liquid and a gas in the same machine, a brief description is provided hereinafter of a portion of a typical conventional pumping unit for multi-phase mixtures, with reference to FIG. 1, wherein the unit as a whole is indicated by the reference number 11.
The unit 11 is designed for pumping of multi-phase mixtures for undersea applications in a vertical configuration.
The pumping unit 11 is of the screw type, and consists of a case 12, in which there are accommodated two screws 14 which engage with one another.
Each of the screws 14 is provided with a cylindrical extension 16, which extends inside a housing 18. In this configuration, the housing 18, which acts as a support, also acts as a tank for the lubrication oil. The extensions 16 are provided with seals 20 and radial axial support bearings 22, which are connected to a thrust bearing 24.
At the end of each extension 16, there is provided a gear 26, which synchronises the motion of the two screws 14. Each of the cylindrical extensions 16 rotates a lubrication pump 30, by means of a coupling 28. There are two pumps 30, in order to guarantee the reliability of the pumping unit 11.
The pumps 30 suck up the oil contained in the housing 18, and keep it circulating in a corresponding lubrication circuit, which is not shown for the sake of simplicity. The lubrication circuit has a connection 32 for delivery to an exchanger (not shown), and a connection 34 for return from the seals and bearings which are disposed in the vicinity of the screws 14.
However, in some cases, these conventional pumping units are unreliable. This is caused mainly by the presence of the lubrication pumps 30, which, if they malfunction, put the entire pumping unit 11 out of use.
Another factor which can detract from the reliability of the pumping unit consists of the presence of the couplings 28, which are also elements which can be subject to faults or breakages.
It is apparent that the possibility of these disadvantages occurring must be limited as far as possible, since, owing to the undersea destination of the pumps, maintenance interventions on them cannot be carried out, or can be carried out only with considerable difficulty, and always at high costs.
It should also be noted that a fault of this type can involve the risk of stoppage of production.
The object of the present invention is to eliminate the technical disadvantages described, by providing a screw-type pumping unit for treatment of fluids in several phases, which is highly reliable, particularly in view of the use for which pumping units of this type are destined.
Another object of the invention is to provide a pumping unit which is substantially economical.
A further object of the invention is to provide a pumping unit for treatment of fluids in several phases, which is substantially simple and dependable.
This object and others, according to the present invention, are achieved by providing a screw-type pumping unit for treatment of fluids in several phases, comprising a pumping chamber, inside which there are accommodated at least two screws, wherein one of the said screws is a drive screw, and supports at one of its ends at least one first gear, which engages with at least one second gear, which is associated with a driven screw, wherein the connection to one another of the said screws permits pumping of a mixture of liquid and gas from at least one intake mouth to at least one outlet mouth, characterised in that the said first and the second gears are contained in a casing which is fitted onto them, and is provided with at least one first through hole, through which oil can be admitted into the said casing, and at least one second through hole, through which the oil can be discharged, such that the said casing, together with the said gears, forms a gear pump which can keep the lubrication oil of the pumping unit circulating.
According to a preferred embodiment, the pumping unit according to the present invention is provided with gears which have at least one transverse groove with two toothed portions, each of which is connected to the corresponding portion of the other gear.
According to another embodiment, the pumping unit according to the present invention is provided with a seal, which is accommodated inside the transverse grooves of the gears. These seals impede reflux of the oil, from one area inside the casing which has high pressure, to another which has a lower pressure.
Further characteristics of the invention are defined in the claims attached to the present patent application.
It should thus be noted that the specific feature of the invention consists of having created a compact structure for accommodation and functioning of the system which permits pumping of the oil destined for lubrication of the machine.
By this means it is possible, inter alia, to eliminate oil pumping components, such as lubrication pumps and corresponding seals, thus permitting elimination of components which were previously critical for the reliability of the system as a whole.
Further characteristics and advantages of a pumping unit for treatment of fluids in several phases according to the present invention, will become more apparent from the following description, provided by way of non-limiting example, with reference to the attached schematic drawings, in which:
FIG. 1 shows a longitudinal cross-section of a screw-type pumping unit for treatment of fluids in several phases, according to the known art;
FIG. 2 shows a longitudinal cross-section of a pumping unit according to the present invention;
FIG. 3 shows a longitudinal cross-section of a detail of the pumping unit shown in FIG. 2;
FIG. 4 shows an enlarged cross-section, produced along line IVxe2x80x94IV in FIG. 3; and
FIG. 5 shows a longitudinal cross-section of a different embodiment of the detail of the pumping unit according to the invention, shown in FIG. 3.